There are many different types of data networks, of which Ethernet is perhaps the best known. Some data networks have resource reservation schemes. One such network is HomePNA (Home Phoneline Network Alliance) v3.0, which is designed to work over existing telephone lines to create a home/small office network. U.S. Pat. No. 7,408,949, issued Aug. 5, 2008 and assigned to the common assignee of the present invention, describes generally how to extend the HomePNA v3.0 standard to operate over such a hybrid network of telephone and coax lines.
HPNA v.3 and other such resource reservation networks have a scheduler, described hereinbelow, to guarantee media resources to network devices, to prevent collision between multiple network devices using the same line and to ensure quality of service. In coax networks, preventive collision detection limits the dynamic range of the network devices, which may impose physical limitations on the size of the network, so it is preferable to use collision avoidance methods for media access in coax networks.
Reference is now made to FIG. 1, which depicts a prior art data network 10, comprising at least two network devices 12 and 14, connected to computers. Network device 12 comprises a modem 16 which includes, among other items, a carrier sensor 20 and a transceiver 24. Network device 14 comprises a modem 18 which includes, among other items, a carrier sensor 20, a scheduler 22 and a transceiver 24. Scheduler 22 creates and sends to each device on network 10 a media access plan (MAP) at the beginning of each transmission cycle. Transceiver 24 either transmits, or both transmits and receives data transmissions over network 10.
An exemplary timing diagram 40 for an exemplary transmission cycle of network 10 (FIG. 1) is shown in FIG. 2, reference to which is now made. Timing diagram 40 shows a detailed schedule of future transmission opportunities (TXOPs) that are made available to specific network devices in the upcoming transmission cycle at specific and non-overlapping times. The start time and length of each scheduled TXOP in the upcoming transmission cycle, such as TXOPs 44, 48 and 50 shown in FIG. 2, as well as the network device to which each TXOP is assigned, is scheduled by scheduler 22 (FIG. 1) in the MAP for the upcoming transmission cycle. The transmission cycle is then initiated, as shown in FIG. 2, with the publication of the MAP by scheduler 22 to the network devices on network 10 (FIG. 1) during MAP publication transmission 30. For example, as shown in timing diagram 40 of FIG. 2, TXOP 44 is shown to be the first TXOP and may be assigned to device 1, TXOP 48 is shown to be the second TXOP and may be assigned to device 2, and TXOP 50 is shown to be the third TXOP and may be assigned to device 3. As shown in timing diagram 40, the MAP for the represented transmission cycle, also includes a scheduled registration TXOP 54 during which new devices may ask to join network 10.
After publication of the MAP during MAP publication transmission 30, device transmissions may begin. Each device recognizes a particular TXOP that has been assigned to it according to the MAP, and either utilizes the TXOP or passes on it.
In timing diagram 40 shown in FIG. 2, it may be seen that device 1 utilizes TXOP 44, as illustrated by hatched area 56 indicating transmission activity of device 1 during TXOP 44. However, if, as shown, devices 2 and 3 do not use TXOPs 48 and 50, these assigned portions of bandwidth are wasted. Furthermore, if no new devices use registration TXOP 54 for registering, the bandwidth of TXOP 54 is also wasted.
As can be seen, the prior art MAP wastes significant resources when scheduled TXOPs for transmission and registration are not fully utilized. Due to the predetermined sizes of the TXOPs, which, at a minimum, are required to be sufficiently large to accommodate at least one data frame, the method suffers from inefficient bandwidth utilization and high per device overhead. Predetermined TXOP size per cycle also means that adaptation of bandwidth change is slow and complex. Small TXOPs relative to transmission burst size may cause Head-Of-Line (HOL) Blocking. Scalability suffers as the network capacity drops with increasing network size. For bi-directional protocols such as TCP and TFTP only low data rates may be achieved due to long round-trip time (RTT).
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.